Illuminating devices of this type are mounted on, for example, an image reading apparatus to be used, and each include a plurality of light-emitting elements (e.g., LEDs) that are arranged in a row and parallel to a main scanning direction for reading a document, and illuminate the document using these light-emitting elements. The image reading apparatus reads the entire document by repeatedly scanning the document being illuminated by the illuminating device along the main scanning direction, while scanning the document also in a sub-scanning direction. The image of the read document is output to a printer or the like to be recorded on a recording sheet.
In this illuminating device, although it is desirable to cause all the light emitted from the light-emitting elements to enter the reading range of the document, actually, it is not possible to cause all the light to enter the reading range of the document, causing light loss, and thus reducing the light loss is desired.
For this reason, in Patent Document 1, a condensing body is provided in the light emission direction of the light-emitting elements such that almost all the light from the light-emitting elements enters the incident-side lens of the condensing body to be emitted from the condensing body toward the reading range of the document, or a prism face is formed in a part of the condensing body or a reflective plate is provided separately from the condensing body such that light transmitted through the condensing body is reflected by the prism face or the reflective plate to be emitted toward the reading range of the document, thereby attempting to reduce the light loss.
Also, in Patent Documents 2 and 3, the light-emitting elements and a light-guiding body are mounted on a substrate, and the light-guiding body is positioned on the light emission side of the light-emitting elements such that light from the light-emitting elements is condensed with the light-guiding body to be emitted toward the reading range of the document, or such that light that has not passed through the light-guiding body is reflected by the reflective plate to be emitted toward the reading range of the document, thereby attempting to reduce the light loss.